Đang chuẩn bị liên kết để tải về tài liệu:
Aerodynamics of helicopter - part 7

Các văn bản kinh điển về khí động học máy bay trực thăng, "Khí động lực học của các máy bay trực thăng" đã được in liên tục cho hơn năm mươi năm. Rõ ràng bằng văn bản và cũng minh họa, cuốn sách tập trung vào mối quan hệ vật lý cơ bản mà không có một sự phát triển toán học rất phức tạp. | 218 AERODYNAMICS OF THE HELICOPTER Basic Performance Equation Helicopter performance analyses like those applied to the airplane are based essentially on curves of power required against airspeed for various flight conditions. In order to obtain curves of this type it is necessary to consider the various sources of power expended by a helicopter in steady flight. These power-absorbing elements are 1 Rotor a Induced power loss b Blade profile-drag loss 2 Parasite drag of the fuselage rotor hub and tail rotor if any 3 The power necessary to change the potential energy of the helicopter at a given rate of speed in the climb or glide condition. The total power required is equal to the sum of all these items. These power expenditures may be expressed by the following relationship HPt0U1 HP HP HP HP 1 Each individual power loss may be expressed as the energy dissipated per second by an equivalent drag force moving at the translational velocity of the aircraft. Thus if p represents the total equivalent drag force not power and Do D Dp and D the equivalent drag forces corresponding to each of the sources of power expenditure then D v HP D v IIP D v HP D V HP PV HPtoat If equation 2 is substituted into equation 1 then p D Di Dp D 2 3 Equation 3 may be made nondimensional by dividing through by the rotor lift L. Thus 4 FORWARD-FLIGHT PERFORMANCE 219 The first two terms of the right side of equation 4 are sometimes combined by the relation wherein DjL is termed the rotor drag-lift ratio. The symbol P L represents the total rotor-shaft power input and is analogous to the drag-lift ratio of an airplane. It is proportional to the drag that would absorb the same power at the velocity along the flight path as the power being supplied through the rotor shaft. Thus P L may be defined as p _ shaft power _ Qữ T VL VL w In a similar manner DỊL 0 DiL p and DỊL C represent the power required to overcome the rotor profile drag the rotor induced drag the parasite drag of the helicopter .